Fix usages of double-splat with keyword arguments before Ruby 2.6

[kke]

Cop disabled in #364

Ruby 2.6 will give a deprecation warning if you use them together like:

def foo(bar: nil, **options)

as described here: https://bugs.ruby-lang.org/issues/14183

[SpComb]

Ruby 2.6 will give a deprecation warning if you use them together like:

I don't think that's what the issue says... my reading is that will continue to work fine, what's being deprecated is treating keyword arguments as a final positional hash:

def foo(a, options)
    ...
end
def bar(b, foo: nil)
    ...
end

foo('a', bar: false) # this will break
bar('b', options) # this will break

[SpComb]

Testing to show that rubocop is giving false positives: https://gist.github.com/SpComb/483b2e36ce80c52aa48f9e76cfe4f612

Based on my understanding of the upcoming ruby3 changes, only 3/4 of the foo(...) usages should be giving warnings in ruby 2.6, but the foo('a', test: true) case isn't. AFAIK all of the bar and asdf usages are fine?

[SpComb]

So if we have any usages like foo that call methods defined to take positional arguments with keyword arguments, then yes, those should be fixed to use real keyword arguments... however, I think there's going to be approximately one million of those kinds of usages throughout our dependency gems, so I wouldn't worry too much about the ones in our own codebase...?

The ruby 2.6 warnings seem to be specific to the foo('a', **options) usage, but the ruby 3 changes seem to also cover usages like foo('a', test: true), which are far more common.